The Germany midfielder has become a crucial part of the BVB side after a meagre start to life at the Westfalenstadion following his 2011 move from Nurnberg, and the former Mainz boss is thrilled with the way his charge has developed.

“Back then, Ilkay was virtually still an advanced youth player. He had only just finished his school exams. We recognised his abilities early on," Klopp told Bild.

"But the fact he is so good has surprised us. In a very good team, Ilkay has come on leaps and bounds.

“He has the necessary calm, the eye [for a pass] and the vision. Ilkay now sees bigger spaces, and can also find them with long balls. Furthermore, he is strong on the ball while knowing when to make a tackle."

Gundogan is currently with the Germany squad ahead of Friday's World Cup qualifier with Kazakhstan.